Dental x-ray tube



Aug. 16, 1932. c. T. ULREY 1,872,335

DENTAL X-RAY TUBE Original Filed June 20 1925 llli INVENTOR CLAYTON T. ULREY ATTORN EY CLAYTON TRIDLE ULREY, or EAST Patented Aug. 16, 1932 UNITED STATES PATENT OFFICE; g

HOUSE LAMP COMPANY,

ORANGE, NEW JERSEY," ASSIGNOR r0 westerns? A CORPORATION or PENNSYLVANIA DENTAL X-RAY TUBE Application ,filed June 20, 1925, Serial No. 38,395. Renewed September 26',

This invention relates toX-ray tubes and more particularly to such tubes adapted for radiographic purposes.

The invention comprises certain improvements in the form of X-ray tube illustrated and described in the patent of Ulreyand Madden, No. 1,715,150 issued May 28, 1929, and an application of Ulrey and Eschholz, Serial No. 1,401 filed January9, 1925.

he present invention relates to an X-ray tube which employsa substantial gas pres sure, means being provided for preventing any detrimentalionization. This is accomplished in the present form of tube by the provision of a reentrant tube of electrical insulating material which surrounds the anode. The reentrant tube is sealed to the glass and the anode is housed therein and closely spaced therefrom thus preventing a discharge from the cathode to the lower portion of the anode through the space between the reentrant tube and the envelope, and also preventing a discharge from taking place through the space between the reentrant tube and the anode.

Another feature of the present invention is in forming the housing which surrounds the anode of a material which is capable of withstanding the high temperatures to which the anode is heated while the gases are being removed therefrom and which possesses good insulating properties. I have found that pyrex, or a silica glass is suitable for this purpose, although quartz may be employed.

The device is particularly adapted for the generation of X-rays along the axis of the tube and in order to accomplish this end, the anode and cathode are arranged in axial alignment with the longitudinal axis of the tube, provision being made for permitting the -rays to pass through the incandescible cathode so as to emerge -from the end of the envelope surroundingthese elements.

In view of the foregoing, it is an object of the present invention to provide an X-ray tube of simple design and comparatively inexpensive to manufacture.

It is another object of myinvention to provide an X-ray tube hav'ng an insulating housing-surroundingthe electrodes of said tube.

vide an X-ray tube'consisting gitudinal sectional View of A further object/of my invention is to provide an X-ray tube with a reentranttube so disposed with respect to the electrodes of the tube, that useful X-rays may be generated without danger of objectionable ionization occurring.

Another object of my invention is to provide an X-ray tube with an insulating and heat-resistant housingwithin the same for the electrodes, said housing also serving to support said electrodes. i

A further object of my invention is to proof a plurality of chambers, said chambers being arranged one within the other, one of said chambers completely housing the electrodes of said tube and at the same time serving to support the same.

Referring to the drawing, Fig. 1 is a lonone form of my lnvention;

Fig. 2 is a longitudinal sectional view of a modified form of my invention; and Fig. 3 is a longitudinal sectional view of still another modification of my invention.

The form of invention as illustrated in Fig. 1 consists of a cylindrical envelope 4: having a rentrant tube 5 sealed at 6 to the envelope, as for example, by fusion. The reentra-nt tube 5 and the envelope 4 are preferably cylindrical in form and are made of a high heat resistant material possessing good insulating properties, such as pyrex, quartz, 'orsilica glass. The tube is open at the end 7 and is provided with a partition 8 having an opening 9. The partition is preferably formed integral with the reentrant tube, although it may be secured therein in any suitable manner. It'is preferable to rather closely space the reentra-nt tube from the cylindrical envelope to repress ionization.

A metal cap 11 preferably of nickel, iron or molybdenum may be secured to the end of the reentrant tube 5 by means of pegs or screws 12. The lower edge of the cap is so disposed with respect to the focal spot as to screen out undesirable Xradia tiontending to emerge from the sides of the tube. Another function of the cap is to repress inverse electron flow. The metal cap is pro- 'path of the electrons.

safety for the electrons pear ;passing over the vided with an opening 13 in axial alignment with the opening 9 in the partition 8.

; Within the reentrant tube 5 and disposed between the partition 8 and the metal cap 11 is an incandescible cathode 14 consisting of one and a half turns of filamentary material such as tantalum. Thecathode formed in the manner just described, has an opening through the center thereof through which the X-rays may pass. The cathode is supported by the reentrant tube 5 andmay be insulated from the metal cap 11 by means of insulating bushings 15 of pyreX, quartz "or silica glass. The ends of the incandescible cathode 1st are connected to leading-in wires 16 which may consist of a suitable material such as molybdenum for sealing into the glass envelope 4. The ends of the leading-in wires 16 are connected to metal cups or contact *caps 17 by soldering or the like.

Disposed within the reentrant tube 5 is an anode 18 consisting of a solid copper rod having a target or focal spot 19 of thorium or the like secured therein as by a threaded connection 20 and pressure. The end 21 Of the anode 18 is preferably disposed adjacent the cathode 14 and spaced therefrom so that the spacing therebetween is less than the mean free path oftheelectrons for thepressure of thegas within said tube, whereby ionization is reducedfto a minimum between the electrodes- .ForeXa-mple, with a gaseous pressure of mercuryv of 1 micron at room temperature (about 25 C.) the mean free is approximately 15 It is preferable to employ a factor of so that the ionization current is neg ligible as compared with the pure electron current and therefore the spacing of the electrodes should not be greater than of the mean free path of the electrons.

The anode 'SlliLHK is preferably cylindrical and its surfaces are closely disposed with respect to the reentrant tube 5. The spacing between the tube 5 and the anode shank should be such that ionization is represse within this space, as a result of the repellant action of the charge upon the surface of the tube and the attractive force of the anode the focal spot, together arge effect of the electrons.

with the space c I have found that when the distance is 5 mm.

no appreciable ionization occurs,

if the pressure is 1 micron.

It is also desirable to make .theanode shank of considerable length so as to provide a long-discharge path for the current, thus preventing the current from surface or through the 'reentrant tube to that part of the tube contacting with the shank. The anode is sup ported by means of the reentrant tube through-a cylindrical sleeve 22 which has a longitudinal slot 23 and one or more slots 24 laterally disposed with respect to said longitudinal slot.

tube by upsetting the glass while hot.

are being generated, other feature of the present invention is that This construction, aside from providing means for securing the anode to the reentrant tube, permits the sleeve to expand while the anode is being heat treated without danger of cracking the reentrant tube. Furthermore, by providing a plurality of slots, a more rigidsupport is obtained.

Projections 25 are formed in the reentrant These projections areadapted to enter slots 28 and by turning .the anode when the projections 25 are opposite the slots 24, the anode may be firmly locked to the rentrant tube. The sleeve 22 is secured to the anode shank by a threaded connection 26 The envelope 4.- is, sealed from the atmosphere by a seal 27 which consists of a tube of glass 27 which has a press 29 through which molybjdenumwire '29 is sealed. The tube is fused to asleeve 31 of glass which is drawn down from the envelopes, an exhaust connection 32 beingprovided to evacuate the envelope. In order to facilitate evacuation from within the space within the reentrant tube 5, a passageway 33 is provided passing through the anode shank: and through. a screw 3a, which latter is employed to secure to the anode shank, a leading-in wire 35 extending from the molybdenum seal wire 29.

base 36 of any standard design. The target 19, the opening 9, the cathode 1st and the opening 13 are disposed in axial alignment with the longitudinal axis of the envelope 4: so that the X-rays generated at the target are directed back along the axis of the electron stream emerging from the cathode 1 f. These X-rays emerge from the envelope through the bulbular end portion 37, which should be formed of glass transparent to X-rays.

By reason of the present construction, it

will be observed that the cathode and anode are insulated from each other and that no electrons are capable of causing ionization through long discharge paths between said electrodes. Furthermore, the close spacing of the anode shank with respect to the re'entrant tube 5 and the positioning'of the target with respect to thecathode'is such, together with the geometrical relationship of these elements, that danger of appreciable ionization, whichwould be detrimental to the operation of the X-ray tube when useful X-rays does not take'place. An-

of positioning the filament so that it is not subjected to great strains, this being due to its position in a weak field within the space between the insulating housing 8 and the metal caps, this space-being charged upto-the same potential as the cathode.

In theform of tube illustrated in Fig. 2, instead of providing anintegral glass partition 8,-an insulating bushing or housing-8 may be provided. This housing may con- Theenvolope lis provided with a suitable Y sist of porcelain and comprises a cylindrical wall 38 and an end wall 39 having an opening 41 therein through which the electrons and X-rays pass. The housing 8 may be secured in position by screws or pegs 12. The other elements of the tube are exactly like those illustrated in F 1.

The modification illustrated in Fig. 3 con-' sists in providing the reentrant tube 5 with a constricted portion 42 and a larger portion 43. The anode shank together with the support therefor from the supporting sleeve 22 are disposed within the larger portion 43 of the reentrant tube while the sleeve 22 directly engages the constricted portion 42 of the reentrant tube.

The advantage of this construction is that it permits the heating of the anode to a high temperature after the tube is sealed from the atmosphere without danger of the support therefor being distorted. In Figs. 1 and 2 this same advantage is had by spacing the lower end of the anode shank from the walls of the rentrant tube where it engages the supporting sleeve.

The envelope is preferably provided with vapor at a substantial pressure, for example, .6 of a micron or greater. The vapor I have found to be most satisfactory is a vapor such as mercury because of the ease of introducing a definite pressure of the same. The mercury is preferably introduced by merely connecting the exhaust line to a vessel containing the mercury, the pressure of which at room temperature, being of the order of 1 micron. The advantage of the construction illustrated and described herein resides in the fact that the tube may be exhausted without employment of liquid air traps or other cooling means employed to prevent the mercur if mercury pumps are used for exhausting, from entering the tube as heretofore a very high vacuum was desired.

A further feature which is obtained with the above described construction, is that of securing a finer focus as shown by pin hole images. The reason why a finer focus is secured is not fully understood, however, several factors may be considered as being effective in securing this result, these being 1) the employment of a substantial sure within the tube, (2) the use of a helical cathode so designed that no dispersive action is exerted upon the electrons and (3) the utilization of a thorium focal spot which apparently is entirely covered with a film of thoria except at the point where the electrons are concentrated.

Although several specific embodiments of the present invention have been described and illustrated, it will be obvious to those skilled in the art that modifications falling within the scope of the appended claims may be made therein.

What is claimed is:

gas presanode in position Within said tube, a cathode disposed adjacent theend of said tube, said cathode consisting of an incandescible filament having an opening therethrough, a target in the end of said anode disposed adjacent said cathode and means interposed between said target and cathode for localizing the electrons emitted by said cathode upon said target and means surrounding said target and cathode and having an opening therein in alignment with said cathode and target for'permitting X-rays to pass along the axis of said electron stream.

2. An X-ray device comprising an enclosing envelope including an anode chamber and a cathode chamber, an anode and a cathode disposed in said chambers in relatively close spaced relationship to each other, a dielectric shield member interposed between said anode and said cathode, said shield member being provided with means to concentrate the electron discharge of said cathode upon a focal spot on said anode along substantially the shortest paths of electric discharge between said anode and cathode, and means to intercept and absorb all X-rays emitted from said anode except those emitted in a preferred direction.

3. An X-ray device comprising an enclosing glass envelope, a reentrant tube section fusibly united at one end to the enclosin glass envelope, an anode disposed in said tube section, an X-ray absorbing member enclosing the end of said tube section, a cathode disposed in said end closure member in relative close spaced relationship to said anode,

a dielectric shield member interposed between said anode and cathode, said shield member being provided with means to concentrate the electron discharge of said cathode upon said anode, and means in said X-ray absorbing member to permit the egress of X- rays therefrom in a preferred direction.

In testimony whereof, I have hereunto subscribed my name this 19th day of June, 1925.

CLAYTON TRIDLE ULREY. 

